The subject matter disclosed herein relates to an exdributor valve for a heat exchanger and to a heat exchanger including an exdributor valve.
In air conditioning and refrigeration systems, proper apportionment of two-phase flow to an evaporator heat exchanger has been a challenging issue for a long time. The difficulty occurs in maintaining the quality (gas-liquid mass fraction) and mass flow of the refrigerant equal for each fin passage inside the heat exchanger. With reference to the prior art device shown in FIG. 1, this is traditionally accomplished with an expansion valve 1. The expansion valve 1 is used to modulate refrigerant flow to the evaporator 2. The expansion valve 1 receives liquid refrigerant (single phase) and substantially reduces the pressure which results in “flashing” of the all-liquid refrigerant (single phase) to a liquid-gas state (two phase). The liquid and gas tend to separate downstream of the expansion point 3 due to inertial and gravitational forces. Tube-fin distributors 4 that are widely used in tube-fin evaporators are located immediately downstream of the expansion valve 1 and distribute the liquid-gas mixture before it can separate. A network of capillary tubes 5 is connected to each outlet port of the tube-fin distributor 4 to prevent cross-talk between each tube and individually routed to each fine passage. Tube-fin distributors are fairly good at maintaining uniform distribution to each fin passage of the evaporator 2.
Use of tube-fin distributors and individual capillary tubes with plate-fin, mini-channel, micro-channel, and brazed plate evaporators is seldom used due to its high labor and material cost associated with affixing each capillary tube to an individual fin passage. With these types of evaporators, piccolo distributors are commonly used and are located within the core of the heat exchanger. The cavity within the piccolo distributor cannot avert separation of the two-phase refrigerant resulting in a non-homogeneous liquid-gas mixture entering each distributor hole.
Many different types of two-phase distributors for plate-fin, mini-channel, micro-channel, brazed plate evaporators have been devised to attempt to equally apportion the amount of liquid and gas to each fin passage. However equal distribution has been historically unachievable, yielding a reduced level of heat transfer of the evaporator (the flow tends to stratify in the distributor and liquid pools at one end of the tube while vapor exists through the other ports). Even customized distributors that have been “tuned” to achieve relatively good distribution for one operating condition will inherently become ineffective for other operating conditions (lacks robustness/is not effective for all the operating condition).
To remedy this situation and obtain proper heat transfer, either a larger evaporator is needed (from an otherwise ideal smaller evaporator) or the temperature/pressure of the refrigerant inside the evaporator must be reduced (increasing the pressure ratio of the compressor) which requires more power usage.